Space-charge dynamic in polyethylene: from dc to ac stress

Time-resolved space-charge profiles obtained in low-density polyethylene under sinusoidal or square ac stress for frequencies going from dc to 10 Hz, temperature from 25 to 50 °C and fields of 30 or 40 kV mm−1 are presented. It is shown that most of the features observed under dc stress (generation of carriers of the two polarities with non-symmetrical amount and velocity) are still active under ac stress. As a matter of fact, it is shown that a negative space charge builds up at 50 °C within the whole insulation bulk even with relatively high stress frequency and for short stressing time (2 h). These results clearly show that space charge has to be considered under ac condition.